Electromotive Force
The maximum potential difference a cell can produce, measured when no current is being drawn.
Formula / equation
emf = E_cathode − E_anode
Unit
V
In depth
Because any current flowing causes a voltage drop across the cell's internal resistance, emf must be measured with a high-resistance voltmeter or a potentiometer that draws essentially nothing. It represents the maximum electrical work per coulomb the cell can deliver.
Examples in the real world
A fresh alkaline cell has an emf of 1.5 V but delivers slightly less under load.